纳米颗粒氧化铈的制备研究

氧化铈由于具备独特的redox性能,在催化剂制备方面倍受关注。本文介绍了水热法、模板剂诱导均相沉淀法制备纳米颗粒氧化铈的合成工艺。在NaOH、NH3反应体系中,120℃、24h可获得肩峰较宽、具有CeO2、Ce3O3固溶峰的纳米结构氧化铈颗粒。粒径在5～15nm,比表面积为128 52m2/g;模板诱导沉淀法在(NH2)2CO为0 44mol、SDS为0 02mol、Ce(NO3)3·6H2O为0 01mol、反应72h,可制备出比表面积为155 08m2/g,粒径为10nm、孔径(poresize)为10 07nm的氧化铈。两种合成方法均可制备出具有催化剂所要求的、较高内比表面积和较好纳米结构相的氧化铈颗粒。     

Rare-earth mediated dihydrogen activation and catalytic hydrogenation

This review covers H-H bond cleavage of dihydrogen(H_2) mediated by structurally well-defined rareearth metal(scandium,yttrium and lanthanides) complexes,and their applications in homogenous catalysis,such as catalytic hydrogenation of unsaturated organic molecules.Depending on the mechanism of the H-H bond cleavage,this review is organized in two parts:(1) σ-bond metathesis,and(2)non-σ-metathesis H_2 activation.The latter is a new trend in this research field and is the emphasis of this review.Converting H_2 into inorganic rare-earth polyhydride complexes,albeit their potential applications as hydrogen-storage materiel,is not in the scope of this review.     

Spectroscopic and chemical-kinetic analysis of the phases of HCCI autoignition and combustion for single- and two-stage ignition fuels

The temporal phases of autoignition and combustion in an HCCI engine have been investigated in both an all-metal engine and a matching optical engine. Gasoline, a primary reference fuel mixture (PRF80), and several representative real-fuel constituents were examined. Only PRF80, which is a two-stage ignition fuel, exhibited a “cool-flame” low-temperature heat-release (LTHR) phase. For all fuels, slow exothermic reactions occurring at intermediate temperatures raised the charge temperature to the hot-ignition point. In addition to the amount of LTHR, differences in this intermediate-temperature heat-release (ITHR) phase affect the fuel ignition quality. Chemiluminescence images of iso-octane show a weak and uniform light emission during this phase. This is followed by the main high-temperature heat-release (HTHR) phase. Finally, a “burnout” phase was observed, with very weak uniform emission and near-zero heat-release rate (HRR). To better understand these combustion phases, chemiluminescence spectroscopy and chemical-kinetic analysis were applied for the single-stage ignition fuel, iso-octane, and the two-stage fuel, PRF80. For both fuels, the spectrum obtained during the ITHR phase was dominated by formaldehyde chemiluminescence. This was similar to the LTHR spectrum of PRF80, but the emission intensity and the temperature were much higher, indicating differences between the ITHR and LTHR phases. Chemical-kinetic modeling clarified the differences and similarities between the LTHR and ITHR phases and the cause of the enhanced ITHR with PRF80. The HTHR spectra for both fuels were dominated by a broad CO continuum with some contribution from bands of HCO, CH, and OH. The modeling showed that the CO+O→CO₂+hν reaction responsible for the CO continuum emission tracks the HTHR well, explaining the strong correlation observed experimentally between the total chemiluminescence and HRR during the HTHR phase. It also showed that the CO continuum does not contribute to the ITHR and LTHR chemiluminescence. Bands of H₂O and O₂ in the red and IR regions were also detected during the HTHR, which the data indicated were most likely due to thermal excitation. The very weak light emission in the “burnout” phase also appeared to be thermal emission from H₂O and O₂.     

DISPERSION OF GAS AND LIQUID IN BUBBLE COLUMNS OF HOMOGENEOUS BUBBLE FLOW REGIME

Mean gas holdup, lateral distribution of gas holdup and axial mixing of gas and liquid were measured in bubble columns of 12 and 19cm i.d. The lateral distribution of gas holdup was strongly dependent on the flow regimes in the column. The axial mixing of liquid in the homogeneous bubble flow regime was much smaller than that in the heterogeneous bubble flow regime, and was not expressed by existing correlations. The axial mixing of liquid in the homogeneous bubble flow and the intermediate flow regime was simulated with a flow model based on the lateral distribution of buoyancy force and the effective viscosity. The axial mixing of gas was larger than that of liquid.     

羧甲基甲壳质金属络合物均相催化性能研究

将甲壳质转化为羧甲基甲壳质,与铂络合后对苯环化合物进行均相催化氢化,找出了最佳反应条件。     

环 F_2+uF_2+…+u~(κ-1)F_2上长为2~s的(1+u)-常循环码的距离分布

研究码字的距离分布是编码理论的一个重要研究方向。该文定义了环R=F2+uF2++uk-1F2上的Homogeneous重量,研究了环R上长为2s的(1+u)-常循环码的Hamming距离和Homogeneous距离。使用了有限环和域的理论,给出了环R上长为2s的(1+u)-常循环码和循环自对偶码的结构和码字个数。并利用该常循环码的结构,确定了环R上长为2s的(1+u)-常循环码的Hamming距离和Homogeneous距离分布。     

Pattern formation in models of fixed-bed reactors

This work reviews and compares spatiotemporal patterns in three models of adiabatic fixed catalytic beds for reactions with oscillatory kinetics: homogeneous and heterogeneous models, which are studied using generic first-order kinetics, and a detailed model of CO oxidation in the monolithic reactor. These three models describe reactors with one, two or all three phases (fluid-, solid- and adsorbed-phases), respectively. Pattern selection is based on the oscillatory or bistable nature of the kinetics and on the nature of fronts. The heterogenous and detailed models may exhibit local bistability while the homogeneous model does not admit this property: a simple conversion between the parameters of the homogeneous and heterogeneous models is suggested.

The spatiotemporal patterns in the reactor can be predicted from the sequence of phase planes spanned by the reactor. Stationary or oscillatory front solutions, oscillatory states that sweep the whole surface or excitation fronts may be realized in the homogeneous and heterogeneous models. The detailed model of the converter may exhibit oscillatory motion, which may be periodic or chaotic, in which typically a hot domain enters the reactor exit and moves quickly upstream; the following extinction occurs almost simultaneously due to strong coupling by convection.     

1D unified mathematical model for environmental flow applied to steady aerated mixed flows

Hydraulic models available in literature are unsuccessful in simulating accurately and efficiently environmental flows characterized by the presence of both air-water interactions and free-surface/pressurized transitions (aka mixed flows). The purpose of this paper is thus to fill this knowledge gap by developing a unified one-dimensional mathematical model describing free-surface, pressurized and mixed flows with air-water interactions. This work is part of a general research project which aims at establishing a unified mathematical model suitable to describe the vast majority of flows likely to appear in civil and environmental engineering (pure water flows, sediment transport, pollutant transport, aerated flows…). In order to tackle this problem, our original methodology consists in both time- and space-averaging the Local Instant Formulation, which includes field equations for each phase taken separately and jump conditions, over a flow cross-section involving a free-surface. Subsequently, applicability of the model is extended to pressurized flows as well. The first key result is an original 1D Homogeneous Equilibrium Model which describes two-phase free-surface flows. It is proven to be fundamentally multiphase, to take into account scale heterogeneities of environmental flow and to be very easy to solve. Next, applicability of this free-surface model is extended to pressurized flows by using the classical Preissmann slot concept. A second key result here is the introduction of an original negative Preissmann slot to simulate sub-atmospheric pressurized flows. The model is then closed by using constitutive equations suitable for air-water flows. Finally, this mathematical model is discretised by means of a finite volume scheme and validated by comparison with experimental results from a physical model in the case of a steady flow in a large scale gallery.     

热力学关系坐标图形记忆法

本文在文献［１－３］的基础上，提出了一种热力学关系坐标图形记忆方法．新方法用简洁的数学关系式对均匀系中的六类热力学关系进行了概括，规则很少，易学易记．通过引入广义力和广义位移，将这种方法进行了推广，得到了适用于弹性系统、表面系统、电介质系统（均匀极化）和磁介质系统（均匀磁化）的热力学关系式。     

LMI conditions for robust stability analysis based on polynomially parameter-dependent Lyapunov functions

The robust stability of uncertain linear systems in polytopic domains is investigated in this paper. The main contribution is to provide a systematic procedure for generating sufficient robust stability linear matrix inequality conditions based on homogeneous polynomially parameter-dependent Lyapunov matrix functions of arbitrary degree on the uncertain parameters. The conditions exploit the positivity of the uncertain parameters, being constructed in such a way that: as the degree of the polynomial increases, the number of linear matrix inequalities and free variables increases and the test becomes less conservative; if a feasible solution exists for a certain degree, the conditions will also be verified for larger degrees. For any given degree, the feasibility of a set of linear matrix inequalities defined at the vertices of the polytope assures the robust stability. Both continuous and discrete-time uncertain systems are addressed, as illustrated by numerical examples.